Gate valves are used to control the flow of various fluids carried inside tubular conduits or pipes. A gate valve typically includes a main body structure with a passageway positioned between and coupling a pair axially-aligned conduits that are bolted to opposite sides of the main body structure. A flat, fluid-impermeable gate with a pair of opposed, substantially planar faces is slidable into the passageway through a slot in the main body structure to selectively occlude the passageway and thereby close the valve.
Gate valves that are used to control the flow of fluids include a seal between the gate and the main body structure to prevent the fluid from leaking, either from the valve or across it when closed. For fluids that include a mixture of solids, referred to as a slurry, an adequate seal between the gate and the main body structure can be difficult to achieve. Slurries arise in many harsh industrial environments, such as wood pulp processing and paper manufacturing, various types of mining including coal and phosphates, and bottom ash removal systems for power station smokestack scrubbers. The solids in such slurries can clog, coat, or damage a seal in many gate valves and thereby allow the fluid to leak.
One bidirectional gate valve seal, described in U.S. Pat. No. 4,846,442 of Clarkson et al., includes a pair of opposed solid resilient sleeve units that compressibly engage each other when the valve is open and engage opposite sides of the gate when the valve is closed. A stiffening ring bonded to each sleeve unit engages a rigid locking ring to hold the sleeve unit in place.
Such a gate valve seal suffers from several disadvantages. The solid resilient sleeve units can be difficult to displace when closing the valve because the design does not include a way to eliminate overcompression of the sleeve from the flange-raised face surfaces of the mating conduit, thereby making the valve difficult to operate. Moreover, pressure against the gate in a valve closed position can displace the resilient sleeve unit on the downstream side and allow a leak between the gate and the upstream resilient sleeve unit.